After nearly losing two houses and quite possibly several cats to run-off waters after recent flooding, I am now a believer in placing wooden shipping pallets under feral houses.* (Of course, dummy me placed the houses where there was run-off water in the first place!) Not only do pallets keep the shelters a few inches off the ground, so they are not as dank and damp, but the cats can hang-out on the ground level without getting their paws wet. Feral Samson LOVES using his pallet as a sunning deck in the nice weather. If I could, I'd install a hammock too!
*Companies that receive inventory on pallets are usually happy to have a few taken off their hands and recycled for the cats.